Why after a reboot, the player does not see the music from the SD card for some time?

Question

Android

Redmi 4 X phone with root rights on board and a slightly different firmware ( https://w3bsit3-dns.com/forum/index.php?showtopic=808033&s...). In the repositories for Magisk, I found a way to put Sony Audio Player on my dialer. I installed it, the repository of the Sony device blank, uploaded the APK file, installed everything, I sit and rejoice. After some time, the phone was rebooted. On subsequent use, I notice that among the last played are only songs from the internal memory. To check, I turned on the track, which is exactly on the memory card and rebooted the phone. The theory was confirmed: immediately after the reboot, all the songs from the phone's memory are in the music library, but those in the memory card are not. But after about five / seven minutes, they reappear, as if nothing had happened. It’s just a shame that you can’t listen to music normally after a reboot, and it’s doubly a shame that all playlists fly off.

Does anyone know what's wrong and how it can be fixed?